1. Field of the Invention
The present invention relates to a high-pressure fluid injection nozzle and more particularly to the shape of such nozzle which ensures more effective action of a cavitation phenomenon by a high-pressure fluid jet under water or other fluid.
2. Description of the Prior Art
So-called high-pressure fluid jet processing techniques have been used in which a fluid under high pressure is injected through a small-diameter orifice and the high-pressure fluid is converted to a high-velocity fluid thereby utilizing the energy of the high-velocity fluid for various processing purposes. These high-pressure fluid jet processing techniques have been mainly used effectively for such purposes as cleaning, peeling, drilling and cutting. While the fluid jet has been mostly used in the air in these applications, the fluid jet has also been used in specific gaseous bodies. Also, as special cases, the fluid jet has been used in water or other fluids as disclosed for example in Japanese Patent No. 1117857 and Japanese Utility Model Registration No. 1436331.
While the high-pressure fluid jet processing techniques have been used in various applications as mentioned above, it has been considered that the energy of an injected high-pressure fluid is decayed by a surrounding fluid at a greater rate when used in a fluid such as water than when used in any gaseous body and how to decrease the rate of energy decay is an important point for enhancing the utilization effect.
Therefore, many different means have been adopted to decrease the decay as far as possible. For instance, attempts have been made such that the distance between the nozzle and an object is decreased, that it is devised so that the fluid supplied to the orifice of the nozzle becomes as nearly like a laminar flow as possible, that a space made of a gaseous body such as air is provided near an object in a fluid, e.g., water and the fluid is injected from the nozzle into the space and so on.
Considering the above-mentioned attempts individually, however, the present states of the art have been such that the desired effect is obtained by increasing the pressure of the injected fluid since these attempts are not easily applicable to objects having many irregularities, do not have much effect in reducing the decay and increase the size of the device. As a result, actually expensive devices employing a high-power high pressure generator, a high pressure resistant pipe member and a nozzle meeting severely defined requirements have inevitably resulted.
On the other hand, it has been known that when a high-pressure fluid jet is injected in another fluid, cavitation is caused by the injected fluid. Various studies have been made to prevent the cavitation since the cavitation causes errosion of the surrounding component parts. Devices utilizing the cavitation, e.g., emulsifying devices have been known in some fields. However, it has been true that the general tendency is toward avoiding the occurrence of cavitation. In this connection, the studies on the mechanism of occurrence of cavitation due to a fluid injected in another fluid has been analyzed by H. Rouse, etc., and it has been known that the cavitation is caused by a velocity variation and a pressure variation in a mixed region of an injected fluid and a surrounding fluid.
As regards the shape of nozzles, nozzles of a so-called convergent-divergent shape have already been used as nozzles for gases and nozzles of the similar shape have been used as nozzles for liquids in some fields for nozzle clogging prevention purposes.